Efficiency fluctuations of a heat engine with noise induced quantum coherences

TL;DR

This paper investigates the efficiency fluctuations of a quantum heat engine with noise-induced coherences, revealing that coherence enhances the constancy of efficiency and identifying a lower bound on efficiency fluctuations.

Contribution

It provides an analytical and numerical analysis of how quantum coherences influence efficiency fluctuations and their constancy in a quantum heat engine.

Findings

Most likely efficiency is independent of noise-induced coherences.

The ratio of coherent to incoherent efficiency cumulants is constant.

Coherence can enhance the constancy of efficiency fluctuations.

Abstract

We analyze the efficiency fluctuations of a coherent quantum heat engine coupled to a unimodal cavity using a standard full-counting statistics procedure. The engine's most likely efficiency obtained by computing the large-deviation function corresponds to the quantum efficiency obtained by defining a useful work obtainable from a steady-state fluctuation theorem. The most likely efficiency is independent of the noise induced coherences. The ratio between coherent and incoherent efficiency cumulants is found to be constant and independent of the stochastic efficiency, which we prove analytically. We also numerically demonstrate that treating the efficiency as a stochastic variable allows the enhancement of constancy only in the presence of coherences. At the engine's most likely efficiency, there is no suppression of the second efficiency cumulant leading to a robust constancy. We also report the existence of a lower bound on the second efficiency cumulant.